Inkjet head and method of manufacturing the same

ABSTRACT

According to one embodiment, an inkjet head comprises a substrate, and a nozzle plate. The substrate includes grooves. The nozzle plate includes nozzles that are formed by laser processing to communicate with the grooves. Electrodes are formed on respective internal surfaces of the grooves. Each of the electrodes is formed of a plurality of metal layers, and includes a flat surface that is apart from the internal surfaces of the grooves. A first inorganic film is superposed on the surfaces of the electrodes. A second inorganic film is superposed on the first inorganic film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Division of application Ser. No. 14/154,250 filedJan. 14, 2014, which is a Division of application Ser. No. 13/411,776filed Mar. 5, 2012, the entire contents of both of which areincorporated herein by reference.

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2011-058378, filed on Mar. 16,2011, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an inkjet head, inwhich nozzles are formed in a nozzle plate by irradiating the nozzleplate adhered to a substrate with laser light, and a method ofmanufacturing the inkjet head.

BACKGROUND

Inkjet heads in which ink is ejected from a plurality of nozzles includea substrate which is formed of a piezoelectric material. The substrateis provided with a plurality of grooves to which ink is supplied. Anelectrode, to which a driving voltage is applied, is formed on aninternal surface of each groove.

Each electrode is covered with a protective film which protects theelectrode from ink. For example, an organic film such as polyparaxyleneis used as the protective film. The probability that pin holes aregenerated in an organic film is smaller than the probability that pinholes are generated in an inorganic film. Therefore, even when varioustypes of ink having electrical conductivity are used, it is possible tosecure electric insulation of the electrode from ink.

According to inkjet heads of the prior art, the nozzles are formed in anozzle plate by irradiating the nozzle plate adhered to the substratewith laser light. The laser light is made incident on the inside of thegrooves directly after the laser light passes through the nozzle plate,and applied onto the protective film which covers the electrodes.

The organic film which forms the protective film disappears and a holeis generated when the organic film receives laser light, and thus aregion of the organic film that receives laser light is damaged. As aresult, the electrode is exposed through the hole which is opened in theorganic film, and it is difficult to maintain electric insulation of theelectrodes from ink. Therefore, in particular, in the case of using inkhaving electrical conductivity, it is inevitable that the electrodes aremelted in an early stage. This reduces the durability of the inkjethead.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an inkjet head according to a firstembodiment;

FIG. 2 is a cross-sectional view of the inkjet head, taken along lineF2-F2 of FIG. 1;

FIG. 3 is a cross-sectional view of the inkjet head, taken along lineF3-F3 of FIG. 2;

FIG. 4 is a cross-sectional view of the inkjet head according to thefirst embodiment;

FIG. 5 is an enlarged cross-sectional view of a part of F5 illustratedin FIG. 3;

FIG. 6 is a cross-sectional view of a state in which a piezoelectricelement is embedded in a substrate structure in the first embodiment;

FIG. 7 is a cross-sectional view of a state in which a plurality of longgrooves are formed in the substrate structure and the piezoelectricelement in the first embodiment;

FIG. 8 is a cross-sectional view illustrating a state where the longgrooves are formed in the piezoelectric element in the first embodiment;

FIG. 9 is a cross-sectional view of a state in which an electrode isformed on an internal surface of each of the long grooves in the firstembodiment;

FIG. 10 is a cross-sectional view of a state where surfaces of theelectrodes are covered with an insulating film in the first embodiment;

FIG. 11 is a cross-sectional view of a state where a protective film issuperposed on the insulating film in the first embodiment;

FIG. 12 is a cross-sectional view of a state where an electrodeprotective layer is formed on a surface of the substrate structure andinternal surfaces of the long grooves in the first embodiment;

FIG. 13 is a cross-sectional view of a state where a top-plate framestructure is adhered to the substrate structure;

FIG. 14 is a cross-sectional view of a state where the substratestructure, to which the top-plate frame structure is adhered, is dividedinto two head blocks in the first embodiment;

FIG. 15 is a cross-sectional view of a state where a nozzle plate beforeformation of nozzles is adhered to a head block in the first embodiment;

FIG. 16 is a cross-sectional view of a state where nozzles are formed inthe nozzle plate adhered to the head block by using laser light in thefirst embodiment;

FIG. 17 is a cross-sectional view of an inkjet head according to asecond embodiment;

FIG. 18 is an enlarged cross-sectional view of a part of F18 illustratedin FIG. 17; and

FIG. 19 is a cross-sectional view of a third embodiment, illustrating apositional relation between an electrode, a smoothing film, aninsulating film, and a protective film.

DETAILED DESCRIPTION

In general, according to one embodiment, an inkjet head comprises asubstrate which is formed of a piezoelectric material, and a nozzleplate which is fixed onto the substrate by an adhesive. The substrateincludes a plurality of grooves. The nozzle plate includes a pluralityof nozzles that are formed by laser processing to communicate with thegrooves. Electrodes, to which a driving voltage is applied, are formedon respective internal surfaces of the grooves. Each of the electrodesis formed of a plurality of metal layers that are superposed to coverthe internal surfaces of the grooves, and includes a flat surface thatis apart from the internal surfaces of the grooves. A first inorganicfilm is superposed on the surfaces of the electrodes. A second inorganicfilm is superposed on the first inorganic film. The second inorganicfilm is soaked in ink that is supplied to the grooves.

First Embodiment

A first embodiment will be explained hereinafter with reference to FIG.1 to FIG. 16.

FIG. 1 and FIG. 2 disclose a shear-mode inkjet head 1 which is used bybeing attached to, for example, a carriage of a printer. The inkjet head1 comprises a substrate 2, a top-plate frame 3, a top plate 4, and anozzle plate 5.

As the substrate 2, it is possible to use, for example, alumina (Al₂O₃),silicon nitride (Si₃N₄), silicon carbide (SiC), aluminum nitride (AlN),or lead zirconate titanate (PZT: Pb(Zr, Ti)O₃).

As illustrated in FIG. 2, the substrate 2 has a rectangular shape whichincludes a front surface 2 a and an end surface 2 b. A piezoelectricelement 7 which serves as an actuator is embedded in the front surface 2a of the substrate 2. As illustrated in FIG. 3, the piezoelectricelement 7 includes two piezoelectric members 8 and 9. The piezoelectricmembers 8 and 9 are superposed on and adhered to each other, and extendin a longitudinal direction of the substrate 2. The piezoelectricelement 7 includes a front surface 7 a and an end surface 7 b.

The front surface 7 a of the piezoelectric element 7 is located on thesame plane as the front surface 2 a of the substrate 2, and exposed tothe outside of the substrate 2. In the same manner, the end surface 7 bof the piezoelectric element 7 is located on the same plane as the endsurface 2 b of the substrate 2, and exposed to the outside of thesubstrate 2. The piezoelectric members 8 and 9 are polarized indirections opposite to each other in a thickness direction of thepiezoelectric members 8 and 9.

As the piezoelectric members 8 and 9, it is possible to use, forexample, lead zirconate titanate (PZT), lithium niobate (LiNbO₃), orlithium tantalate (LiTaO₃). In the present embodiment, a highpiezoelectric constant PZT is adopted as the piezoelectric members 8 and9. In addition, a PZT with a dielectric constant lower than that of thepiezoelectric members 8 and 9 is used as a material of the substrate 2,in consideration of the difference in the coefficient of expansionbetween the substrate 2 and the piezoelectric members 8 and 9 and thedielectric constants.

As illustrated in FIG. 2 to FIG. 4, the piezoelectric element 7 isprovided with a plurality of long grooves 11 and a plurality ofpartition walls 12. The long grooves 11 are opened to the front surface7 a and the end surface 7 b of the piezoelectric element 7, and arrangedin a line at intervals in a longitudinal direction of the piezoelectricelement 7. According to the present embodiment, each long groove 11 hasa depth of 300 μm, and a width of 80 μm. In addition, the long grooves11 are arranged in parallel with each other at pitches of, for example,169 μm.

As a result, in the substrate 2 of the present embodiment, an aspectratio which is determined by a ratio (depth/width) of the depth to thewidth of the long grooves 11 is 3.75. Specifically, the aspect ratioincreases when the depth of the long grooves 11 is increased and thewidth thereof is decreased. The aspect ratio and the intervals of thelong grooves 11 are determined to desired values, according to theresolution and ink ejection amount required for the inkjet head 1.

In addition, each of the partition walls 12 of the piezoelectric element7 is interposed between two adjacent long grooves 11, and separates thelong grooves 11 from each other.

As illustrated in FIG. 2, each long groove 11 includes an extended part13. The extended part 13 is extended from one end part of the longgroove 11, which runs along the longitudinal direction of the longgroove 11, toward the substrate 2. The extended part 13 is opened to thefront surface 2 a of the substrate 2, and has a depth which graduallydecreases with increasing distance from the piezoelectric element 7.Therefore, a distal end of the extended part 13 of each long groove 11is connected to the front surface 2 a of the substrate 2.

The top-plate frame 3 is fixed onto the front surface 2 a of thesubstrate 2 by means such as bonding. The top-plate frame 3 includes afront frame part 14. The front frame part 14 is superposed on thepiezoelectric element 7, and extends along a direction in which the longgrooves 11 are arranged. The front frame part 14 closes an opening endof each long groove 11, which is opened to the front surface 2 a of thesubstrate 2. In addition, the front frame part 14 includes an endsurface 14 a. The end surface 14 a is located on the same plane as theend surface 2 b of the substrate 2 and the end surface 7 b of thepiezoelectric element 7.

The top plate 4 is superposed on the top-plate frame 3, and fixed ontothe top-plate frame 3 by means such as bonding. A region which isenclosed by the top plate 4, the top-plate frame 3, and the frontsurface 2 a of the substrate 2 forms a common pressure chamber 15. Thetop plate 4 includes a plurality of ink supply holes 16. The ink supplyholes 16 supply ink to the common pressure chamber 15.

According to the present embodiment, the extended part 13 of each longgroove 11 opened to the front surface 2 a of the substrate 2 is exposedto the common pressure chamber 15. Therefore, each long groove 11communicates with the common pressure chamber 15 through the extendedpart 13.

As illustrated in FIG. 1, FIG. 2, and FIG. 4, the nozzle plate 5 isadhered onto the end surface 2 b of the substrate 2 b, the end surface 7b of the piezoelectric element 7, and the end surface 14 a of the frontframe part 14 by an adhesive 18. The nozzle plate 5 is formed of, forexample, a polyimide film. The polyimide film has a thickness of 50 μm.The nozzle plate 5 closes the opening ends of the long grooves 11, whichare opened to the end surface 7 b of the piezoelectric element 7.

Regions which are enclosed by internal surfaces of the respective longgrooves 11, the front frame part 14 of the top-plate frame 3, and thenozzle plate 5 form a plurality of pressure chambers 19. The pressurechambers 19 are arranged in a line at intervals in the longitudinaldirection of the piezoelectric member 7, and communicate with the commonpressure chamber 15.

As illustrated in FIG. 2 and FIG. 3, the nozzle plate 5 includes aplurality of nozzles 21. The nozzles 21 are minute holes of a micronsize, which pierce the nozzle plate 5 in a thickness direction of thenozzle plate 5. The nozzles 21 are formed by subjecting the nozzle plate5 to laser processing using, for example, an excimer laser device. Thenozzles 21 are arranged in a line at predetermined intervals toindividually communicate with the pressure chambers 19, and opposed to arecording medium to be printed.

In the present embodiment, a position of focus F of laser light which isoutput from an excimer laser device is shifted to the outside of thenozzle plate 5, as illustrated in FIG. 4. Thereby, the laser lightspreads toward each pressure chamber 19 when it pierces through thenozzle plate 5.

As a result, each of the nozzles 21 which are processed by laser lightis formed to have a tapered shape, a diameter of which is graduallyincreased toward the pressure chamber 19. In each of the nozzles 21 ofthe present embodiment, a diameter of an upstream end which is opened tothe pressure chamber 19 is 50 μm, and a diameter of an ejection endwhich is opened to a side opposite to the pressure chamber 19 is 30 μm.

As illustrated in FIG. 4, part of the adhesive 18 which fills the spacebetween the end surface 7 b of the piezoelectric member 7 and the nozzleplate 5 enters the pressure chambers 19 as surplus parts 20. The surplusparts 20 of the adhesive 18 are cured in a state of adhering onto asurface of the nozzle plate 5, which faces the pressure chambers 19, andbeing adjacent to the opening ends of the nozzles 21 in the pressurechambers 19.

In addition, cut parts 22 are formed in the surplus parts 20 of theadhesive 18. The cut parts 22 are parts which are left after the laserlight to form the nozzles 21 passes through the surplus parts 22. Thecut parts 22 are inclined to be aligned with internal surfaces of thenozzles 21. Specifically, as illustrated by two-dot chain lines in FIG.4, for example, when an end part 20 a of any surplus part 20 projectsinto the pressure chamber 19 at the opening end of the nozzle 21, theend part 20 a is removed by laser light which pierces the nozzle plate5. Therefore, the upstream end of the nozzle 21 is not partly coveredwith the adhesive 18.

The long grooves 11 which define the pressure chambers 19 are formed bysubjecting the piezoelectric member 7 to cutting using, for example, adiamond cutter. Therefore, as illustrated in FIG. 3 and FIG. 4, each ofinternal surfaces of the long grooves 11 which define the pressurechambers 19 has a number of depressions and projections 23 of a micronsize. In addition, the piezoelectric member 7 formed of PZT is fragile.Thereby, in the process of cutting the piezoelectric member 7, theinternal surfaces of the long grooves 11 may be partly lacking. As aresult, the internal surfaces of the long grooves 11 which have beensubjected to cutting become rough surfaces which lack smoothness.

Electrodes 25 are formed on respective internal surfaces of the longgrooves 11. Electrodes 25 of two adjacent long grooves 11 are separatedfrom each other to be electrically independent of each other. Asillustrated in FIG. 5, each electrode 25 is formed of a copper platinglayer 26 and a nickel plating layer 27. The copper plating layer 26 isan example of a first metal layer. The nickel plating layer 27 is anexample of a second metal layer. The copper plating layer 26 forms anundercoat of the electrode 25.

The copper plating layer 26 of the present embodiment has a two-layerstructure including an electroless copper plating layer 28 a and anelectrolytic copper plating layer 28 b. The electroless copper platinglayer 28 a is formed by subjecting the surface 2 a of the substrate 2and the internal surfaces of the long grooves 11 to electroless copperplating. The electroless copper plating layer 28 a forms a predeterminedelectrode pattern for each long groove 11. The electrolytic copperplating layer 28 b is formed by subjecting the surface 2 a of thesubstrate 2 and the internal surfaces of the long grooves 11 toelectrolytic copper plating. The electrolytic copper plating layer 28 bis superposed on the electroless copper plating layer 28 a.

The nickel plating layer 27 is formed by subjecting the copper platinglayer 26 to electrolytic nickel plating. The nickel plating layer 27 issuperposed on the copper plating layer 26 to cover the copper platinglayer 26.

The copper plating layer 26 has a function of absorbing the depressionsand projections 23 generated on the internal surfaces of the longgrooves 11. Therefore, the nickel plating layer 27 which covers thecopper plating layer 26 has a flat surface. Therefore, the surface 25 aof each electrode 25 which is separated from the internal surface ofeach long groove 11 is flattened, and pointed projections are removedfrom the surface 25 a. An average surface roughness of the surface 25 aof each electrode 25 is preferably 0.6 μm or less.

As illustrated in FIG. 2, each electrode 25 includes a conductor pattern30. The conductor pattern 30 is guided to the surface 2 a of thesubstrate 2 through the common pressure chamber 15. The conductorpattern 30 is drawn out of the top-plate frame 3, and electricallyconnected to a tape carrier package 31. A driving circuit 32 whichdrives the inkjet head 1 is mounted onto the tape carrier package 31.

The driving circuit 32 applies a driving pulse (driving voltage) to theelectrodes 25 of the inkjet head 1. Thereby, a difference in potentialis generated between electrodes 25, which are adjacent to each otherwith the pressure chamber 19 interposed therebetween, and an electricfield is generated in the partition walls 12 which correspond to theelectrodes 25. As a result, the partition walls 12, which are adjacentto each other with the pressure chamber 19 interposed therebetween,shear and are curved to increase the volume of the pressure chamber 19.

When the polarity of the driving pulse applied to the electrodes 25 isreversed, the partition walls 12 return to their initial shapes. Byreturning the partition walls 12 to their initial shapes, ink which issupplied from the common pressure chamber 15 to the pressure chamber 19is pressurized. Part of the pressurized ink is changed to ink drops andejected from the nozzles 21 toward the recording medium.

As illustrated in FIG. 3 to FIG. 5, each electrode 25 is covered with anelectrode protective layer 33. The electrode protective layer 33 has atwo-layer structure including an insulating film 34 and a protectivefilm 35. The insulating film 34 is an example of a first inorganic film.The insulating film 34 is formed of an inorganic insulating materialsuch as silicon dioxide (SiO₂). The insulating film 34 is superposed onthe flat surface 25 a of the electrode 25. The insulating film 34preferably has a thickness of 1.0 μm or more.

The protective film 35 is an example of a second inorganic film. Theprotective film 35 is formed of an inorganic insulating material such ashafnium oxide (HfO₂). The protective film 35 is superposed on a surfaceof the insulating film 34, and covers the insulating film 34. Therefore,the protective film 35 is exposed to the inside of each pressure chamber19, to be soaked in ink supplied to the pressure chamber 19. Theprotective film 35 preferably has a thickness of 50 nm or more.

According to the inkjet head 1 of the first embodiment, laser lightwhich forms the nozzles 21 pierces the nozzle plate 5 and is madeincident on each pressure chamber 19, as illustrated in FIG. 4. Sincethe laser light spreads from the nozzle plate 5 toward the pressurechamber 19, part of the laser light is applied onto the protective film35 which covers the electrode 25.

The protective film 35 and the insulating film 34 which are formed ofinorganic insulating materials are difficult to be damaged byirradiation of laser light. Therefore, each electrode 25 is maintainedin a state of being electrically insulated from ink supplied to thepressure chamber 19. Therefore, even when the ink has electricalconductivity, it is possible to prevent corrosion of the electrodes 25and electric decomposition of ink due to flow of a current through theink.

On the other hand, the insulating film 34 and the protective film 35which are formed of inorganic insulating materials are easily influencedby surface roughness of the electrodes 25. Specifically, when thesurface roughness of the electrodes 25 increases, pin holes may begenerated in the insulating film 34 and the protective film 35.

In the first embodiment, the undercoat of the electrodes 25 is formed ofthe copper plating layer 26. The copper plating layer 26 has a functionof absorbing the many depressions and projections 23 of a micron size,which are generated on the internal surfaces of the long grooves 11, andsmoothing the internal surfaces of the long grooves 11. Therefore, thesurface 25 a of each electrode 25 is a flat surface, from which pointedprojections that cause pin holes are removed. Therefore, pin holes arehardly generated in the insulating film 34 and the protective film 35which are superposed on the surface 25 a of each electrode 25.

In addition, even when pin holes are generated in the insulating film 34deposited on the surface 25 a of the electrode 25, the pin holes of theinsulating film 34 can be covered with the protective film 35 depositedon the insulating film 34.

Consequently, even in the structure of forming the nozzles 21 byirradiating the nozzle plate 5 adhered onto the substrate 2 with laserlight, it is possible to maintain electrical insulation of theelectrodes 25 from ink, and avoid corrosion of the electrodes 25 andelectrical decomposition of ink. Therefore, it is possible to obtain theinkjet head 1 which has a good printing quality and excellentdurability.

The inventor(s) of the present embodiment performed the followingexperiment, using the inkjet head 1 in which an average surfaceroughness of the surfaces 25 a of the electrodes 25 was 0.6 μm or less.In the experiment, several types of inorganic insulating materials whichformed the insulating film 34 were prepared, and whether the insulatingfilm 34 included any pin holes when the thickness of each inorganicinsulating material was changed within a range of 1.0 μm to 5.0 μm waschecked.

As a result, no pin holes were recognized, as long as the thickness ofthe insulating film 34 fell within the range of 1.0 μm to 5.0 μm.Therefore, to eliminate pin holes from the insulating film 34, it isdesired to set the thickness of the insulating film 34 formed of aninorganic insulating material to 1.0 μm or more. More preferably, theinsulating film 34 has a thickness of 3 μm or more.

Next, a process of manufacturing the inkjet head 1 of the firstembodiment will be explained, with reference to FIG. 6 to FIG. 16.

First, two piezoelectric members 8 and 9 are adhered to each other, andthereby a piezoelectric element 7 which has reversed polarizingdirections is formed. Thereafter, a substrate structure 41 asillustrated in FIG. 6 is prepared. The substrate structure 41 has a sizetwice as large as the substrate 2, and a depressed part 42 is formed ina center part of a surface of the substrate structure 41. PZT, which hasa dielectric constant lower than that of the piezoelectric element 7, isused as the substrate structure 41. Then, the piezoelectric element 7 isembedded in and adhered to the depressed part 42 of the substratestructure 41.

Thereafter, the piezoelectric element 7 is subjected to cutting by usinga disk-shaped diamond cutter, and thereby a plurality of long grooves 11as illustrated in FIG. 8 and FIG. 9 are formed in the piezoelectricelement 7. In the present embodiment, a diamond cutter which has a facewidth of 80 μm is used as the diamond cutter. Therefore, the width ofeach long groove 11 is 80 μm. The depth of each long groove 11 isdetermined by a moving quantity of the diamond cutter along a thicknessdirection of the piezoelectric element 7. In the present embodiment, thedepth of each long groove 11 is 300 μm. The internal surface of eachlong groove 11 is a rough surface which includes many depressions andprojections 23.

As illustrated in FIG. 7, when the long grooves 11 are formed in thepiezoelectric element 7, the surface of the substrate structure 41 isscraped off in a shape of grooves by the diamond cutter. Parts of thesubstrate structure 41 which are scraped off by the diamond cutterfunction as extended parts 13, each of which has a gradually decreasingdepth.

Thereafter, an electroless copper plating layer 28 a is formed on theinternal surfaces of the long grooves 11 including the extended parts 13and the surface of the substrate structure 41. Thereafter, anelectrolytic copper plating layer 28 b is formed on the electrolesscopper plating layer 28 a. Thereby, a copper plating layer 26 serving asan undercoat is formed on the internal surfaces of the long grooves 11.

In addition, a nickel plating layer 27 is formed on the electrolyticcopper plating layer 28 b serving as a surface layer of the copperplating layer 26. Thereby, an electrode 25 having a two-layer structureand a conductor pattern 30 are formed on the internal surface of eachlong groove 11.

The copper plating layer 26 levels the internal surface of each longgroove 11 having many depressions and projections 23. As a result, thenickel plating layer 27 which covers the copper plating layer 26 has aflat surface. Therefore, the surfaces 25 a of the electrodes 25 whichare apart from the internal surfaces of the long grooves 11 areflattened, and an average surface roughness of the surfaces 25 a of theelectrodes 25 is 0.6 μm or less.

Thereafter, parts of each electrode 25, which are formed on uppersurfaces of the partition walls 12 that partition adjacent long grooves11, are removed from the upper surfaces of the partition walls 12 bymeans such as grinding.

Next, as illustrated in FIG. 10, an insulating film 34 is formed on theelectrodes 25 in the long grooves 11. Silicon dioxide, which is anexample of an inorganic insulating material, is used as the insulatingfilm 34. The insulating film 34 is formed by, for example, PE-CVD(Plasma-Enhanced Chemical Vapor Deposition). The insulating film 34 hasa thickness of 1.0 μm or more.

The inorganic insulating material which forms the insulating film 34 isnot limited to silicon dioxide. As the inorganic insulating material,for example, it is possible to use Al₂O₃, SiN, ZnO, MgO, ZrO₂, Ta₂O₅,Cr₂O₃, TiO₂, Y₂O₃, YBCO, mullite (Al₂O₃.SiO₂), SrTiO₃, Si₃N₄, ZrN, AlN,or Fe₃O₄.

As the method of forming the insulating film 34, it is possible to use,for example, MBE (Molecular Beam Epitaxy), AP-CVD (Atmospheric-PressureChemical Vapor Deposition), ALD (Atomic-Layer Deposition), orapplication, as well as PE-CVD. In other words, the method of formingthe insulating film 34 is not limited, as long as the inorganicinsulating material can be deposited on the nickel plating layer 27 byreacting or condensing the inorganic insulating material including SiO₂on the nickel plating layer 27 in a vacuum or the atmosphere.

When the insulating film 34 is formed, part of the conductor pattern 30which is guided to the surface of the substrate structure 41 is masked.Thereby, the insulating film 34 is prevented from being formed on partof the conductor pattern 30, to which the tape carrier package 31 isconnected.

Then, as illustrated in FIG. 11 and FIG. 12, a protective film 35 isformed on the insulating film 34. Hafnium oxide (HfO₂), which is anexample of the inorganic insulating material, is used as the protectivefilm 35. The protective film 35 is formed by, for example, ALD(Atomic-Layer Deposition). The protective film 35 has a thickness of 50nm or more.

The inorganic insulating material which forms the protective film 35 isnot limited to hafnium oxide, but may be, for example, Al₂O₃, or SiO₂.

As the method of forming the protective film 35, it is possible to useAP-CVD (Atmospheric-Pressure Chemical Vapor Deposition), as well as ALD.In other words, the method of forming the protective film 35 is notlimited, as long as the inorganic insulating material can be depositedon the insulating film 34 by reacting or condensing the inorganicinsulating material including hafnium oxide on the insulating film 34 ina vacuum or the atmosphere.

In addition, when the protective film 35 is formed, part of theconductor pattern 30 which is guided to the surface of the substratestructure 41 is masked. Thereby, the protective film 35 is preventedfrom being formed on the part of the conductor pattern 30 to which thetape carrier package 31 is connected.

Thereafter, as illustrated in FIG. 13, a top-plate frame structure 43 isfixed on a surface of the substrate structure 41 by means such asbonding. The top-plate structure 43 includes a frame part 44 and acenter part 45. The frame part 44 is superposed on an outer peripheralpart of the surface of the substrate structure 41. The center part 45 issurrounded by the frame part 44, and superposed on the piezoelectricelement 7 in which the long grooves 11 are formed. Therefore, the centerpart 45 closes the opening end of each long groove 11.

Thereafter, as illustrated in FIG. 14, the substrate structure 41, towhich the top-plate frame structure 43 is adhered, is subjected tocutting using a diamond cutter or the like. Thereby, the substratestructure 41 is divided into two together with the top-plate framestructure 43. As a result, a pair of head blocks 46 a and 46 b, in eachof which the substrate 2 is united with the top-plate frame 3, areformed. In each of the head blocks 46 a and 46 b, the end surface 2 b ofthe substrate 2, the end surface 7 b of the piezoelectric element 7, andthe end surface 14 a of the front frame part 14 of the top-plate frame 3are located at a divided end of each of the head blocks 46 a and 46 b,and located on the same plane.

Thereafter, as illustrated in FIG. 15 which shows one head block 46 a asa representative, a nozzle plate 5 before formation of nozzles isadhered to spread over the end surface 2 b of the substrate 2, the endsurface 7 b of the piezoelectric element 7, and the end surface 14 a ofthe front frame part 14 of the top-plate frame 3. As a result, aplurality of pressure chambers 19 are formed between the respective longgrooves 11 of the substrate 2 and the front frame part 14 of thetop-plate frame 3.

Surplus parts 20 of adhesive 18 which fills the space between the endsurface 7 b of the piezoelectric element 7 and the nozzle plate 5 enterthe pressure chambers 19. The surplus parts 20 of the adhesive 18 areleft as a thin film on a surface of the nozzle plate 5 which faces thepressure chambers 19.

Thereafter, as illustrated in FIG. 4 and FIG. 16, the nozzle plate 5 issubjected to laser processing using, for example, an excimer laserdevice, and thereby a plurality of nozzles 21 are formed in the nozzleplate 5. Specifically, the nozzle plate 5 is irradiated with laser lightfrom a side opposite to the pressure chambers 19. Thereby, parts of thenozzle plate 5 formed of a polyimide film, which are irradiated with thelaser light, are chemically decomposed and changed to the nozzles 21.

As illustrated in FIG. 4, the focus F of the laser light is locatedoutside the nozzle plate 5. Therefore, the laser light spreads in aflare shape toward each pressure chamber 19. Therefore, each nozzle 21has a tapered shape, with a diameter continuously increasing toward thecorresponding pressure chamber 19.

The laser light pierces the nozzle plate 5 in a thickness direction, andthereafter is made incident on each pressure chamber 19. The protectivefilm 35 which is exposed to the inside of each pressure chamber 19 isirradiated with the laser light in the vicinity of the nozzle 21.

The protective film 35 which is formed of an inorganic insulatingmaterial is difficult to be damaged by irradiation of laser light.Therefore, no holes are generated in a region of the protective film 35irradiated with laser light.

The end part 20 a of each surplus part 20 of the adhesive 18 may projectto a region in which a nozzle 21 is to be formed in the pressure chamber19, before the nozzles 21 are formed in the nozzle plate 5. The end part20 a of each surplus part 20 is removed by laser light, when the laserlight pierces the nozzle plate 5 and is made incident on the pressurechamber 19.

Consequently, the surplus parts 20 of the adhesive 18 do not close thenozzles 21. Therefore, the surplus parts 20 of the adhesive 18 do notaffect the flow of ink which is ejected from the nozzles 21, and it ispossible to maintain a good printing quality.

Second Embodiment

FIG. 17 and FIG. 18 disclose a second embodiment.

The second embodiment is different from the first embodiment in astructure of the electrodes and the electrode protective layer. Thestructure of the other parts of the inkjet head of the second embodimentis the same as the first embodiment. Therefore, in the secondembodiment, constituent elements which are the same as those of thefirst embodiment are denoted by the same respective reference numeralsas those of the first embodiment, and explanation thereof is omitted.

As illustrated in FIG. 18, each electrode 50 is formed of a nickelplating layer 51 and a gold plating layer 52. The nickel plating layer51 is an example of the first metal layer. The gold plating layer 52 isan example of the second metal layer. The nickel plating layer 51 formsan undercoat of the electrode 50.

The nickel plating layer 51 is superposed on an internal surface of eachlong groove 11, and forms a predetermined electrode pattern for eachlong groove 11. The gold plating layer 52 is superposed on the nickelplating layer 51, and covers the nickel plating layer 51.

The nickel plating layer 51 and the gold plating layer 52 are inferiorto the copper plating layer 26 of the first embodiment, in the functionof flattening the internal surface of each long groove 11. In otherwords, a surface 50 a of each electrode 50 is not smooth due to theinfluence of depressions and projections 23 which are generated on theinternal surface of the long groove 11.

Each electrode 50 is covered with an electrode protective layer 53. Theelectrode protective layer 53 has a three-layer structure including asmoothing film 54, an insulating film 55, and a protective film 56. Thesmoothing film 54 is an example of a first inorganic film. The smoothingfilm 54 is formed of an inorganic insulating material such asSiragusital. The smoothing film 54 has a thickness with which thesmoothing film 54 can absorb the depressions and projections generatedon the surface 50 a of each electrode 50.

Therefore, a surface 54 a of the smoothing film 54 which is apart fromthe electrode 50 is flattened, and pointed projections are removed fromthe surface 54 a. The surface 54 a of the smoothing film 54 preferablyhas an average surface roughness of 0.6 μm or less.

The insulating film 55 is an example of a second inorganic film. Theinsulating film 55 is formed of an inorganic insulating material such assilicon dioxide (SiO₂). The insulating film 55 is superposed on thesurface 54 a of the smoothing film 54. The insulating film 55 preferablyhas a thickness of 1.0 μm or more.

The protective film 56 is an example of a third inorganic film. Theprotective film 56 is formed of an inorganic insulating material such ashafnium oxide (HfO₂). The protective film 56 is superposed on a surfaceof the insulating film 55, and covers the insulating film 55. Therefore,the protective film 56 is exposed to the inside of each pressure chamber19, and soaked in ink which is supplied to each pressure chamber 19. Theprotective film 56 preferably has a thickness of 50 nm or more.

The second embodiment is different from the first embodiment in theprocess of forming the electrodes 50 and the electrode protective layer53. The other parts of the process of manufacturing the inkjet head 1are the same as those of the first embodiment. Therefore, in the secondembodiment, only the process of forming the electrodes 50 and theelectrode protective layer 53 is explained.

After long grooves 11 are formed in a piezoelectric element 7, a nickelplating layer 51 is formed. The nickel plating layer 51 is obtained bysubjecting internal surfaces of the long grooves 11 and a surface of asubstrate structure 41 to electroless nickel plating. Then, a goldplating layer 52 is formed on the nickel plating layer 51. The goldplating layer 52 is obtained by subjecting the nickel plating layer 51to electrolytic gold plating. Thereby, an electrode 50 which has atwo-layer structure as illustrated in FIG. 18 is formed on the internalsurface of each long groove 11.

Thereafter, parts of the electrodes 50 which are formed on uppersurfaces of partition walls 12 that partition adjacent long grooves 11are removed from the upper surfaces of the partition walls 12 by meanssuch as grinding.

Then, a smoothing film 54 is formed on the electrodes 50 of the longgrooves 11. Siragusital, which is an example of the inorganic insulatingmaterial, is used as the smoothing film 54. The smoothing film 54 isobtained by applying Siragusital in a liquid phase to the surfaces 50 aof the electrodes 50 and thereafter curing the Siragusital at normaltemperature.

Specifically, the smoothing film 54 is applied to the surfaces 50 a ofthe electrodes 50, with a thickness to set an average surface roughnessof the surface 54 a which is apart from the electrodes 50 to 0.6 μm orless. The thickness of the smoothing film 54 differs according to thetype of the inorganic insulating material used.

By virtue of the existence of the smoothing film 54 having the abovestructure, the depressions and projections generated on the surface 50 aof each electrode 50 are absorbed, and the surface 54 a of the smoothingfilm 54 is flattened.

As the material which forms the smoothing film 54, it is possible to usea liquid which is obtained by dissolving, for example, nanosilica in anorganic solvent. The method of forming the smoothing film 54 is notlimited to application, but may be, for example, a Sol-Gel process,Spray process, or electrodeposition process. In other words, the methodof forming the smoothing film 54 is not limited, as long as the liquidcan be adhered to the electrodes 50 that are formed inside the longgrooves 11 and the liquid can be cured.

Thereafter, an insulating film 55 is formed on the smoothing film 54.Silicon dioxide, which is an example of the inorganic insulatingmaterial, is used as the insulating film 55. The insulating film 55 isformed by, for example, PE-CVD (Plasma-Enhanced Chemical VaporDeposition). The insulating film 55 has a thickness of 1.0 μm or more.

The inorganic insulating material which forms the insulating film 55 isnot limited to silicon dioxide. As the inorganic insulating material, itis possible to use, for example, Al₂O₃, SiN, ZnO, MgO, ZrO₂, Ta₂O₅,Cr₂O₃, TiO₂, Y₂O₃, YBCO, mullite (Al₂O₃.SiO₂), SrTiO₃, Si₃N₄, ZrN, AlN,or Fe₃O₄.

As the method of forming the insulating film 55, it is possible to use,for example, MBE (Molecular Beam Epitaxy), AP-CVD (Atmospheric-PressureChemical Vapor Deposition), ALD (Atomic-Layer Deposition), orapplication, as well as PE-CVD. In other words, the method of formingthe insulating film 55 is not limited, as long as the inorganicinsulating material can be deposited on the smoothing film 54 byreacting or condensing the inorganic insulating material including SiO₂on the smoothing film 54 in a vacuum or the atmosphere.

When the insulating film 55 is formed, part of the conductor pattern 30which is guided to the surface of the substrate structure 41 is masked.Thereby, the insulating film 55 is prevented from being formed on thepart of the conductor pattern 30 to which a tape carrier package 31 isconnected.

Then, a protective film 56 is formed on the insulating film 55. Hafniumoxide (HfO₂), which is an example of the inorganic insulating material,is used as the protective film 56. The protective film 56 is formed by,for example, ALD (Atomic-Layer Deposition). The protective film 56 has athickness of 50 nm or more.

The inorganic insulating material which forms the protective film 56 isnot limited to hafnium oxide, but may be, for example, Al₂O₃, or SiO₂.

As the method of forming the protective film 56, it is possible to useAP-CVD (Atmospheric-Pressure Chemical Vapor Deposition) or the like, aswell as ALD. In other words, the method of forming the protective film56 is not limited, as long as the inorganic insulating material can bedeposited on the insulating film 55 by reacting or condensing theinorganic insulating material including hafnium oxide on the insulatingfilm 55 in a vacuum or the atmosphere.

In addition, when the protective film 56 is formed, part of theconductor pattern 30 which is guided to the surface of the substratestructure 41 is masked. Thereby, the protective film 56 is preventedfrom being formed on the part of the conductor pattern 30 to which thetape carrier package 31 is connected.

According to the second embodiment, the smoothing film 54 which isapplied to the surface 50 a of each electrode 50 absorbs manydepressions and projections generated on the surface 50 a of eachelectrode 50. Therefore, the surface 54 a of the smoothing film 54 whichis apart from each electrode 50 is a flat surface, from which pointedprojections that cause pin holes are removed. Therefore, pin holes arehardly generated in the insulating film 55 and the protective film 56.

In addition, even when pin holes are generated in the insulating film55, the protective film 56 superposed on the insulating film 55 cancover the pin holes generated in the insulating film 55. Consequently,it is possible to maintain electrical insulation of the electrodes 50from ink by using the electrode protective layer 53 having thethree-layer structure, and avoid corrosion of the electrodes 50 andelectrical decomposition of ink. Therefore, it is possible to obtain theinkjet head 1 with good printing quality and excellent durability, inthe same manner as the first embodiment.

Third Embodiment

FIG. 19 discloses a third embodiment.

The third embodiment is obtained by combining the electrodes of thefirst embodiment with the electrode protective layer of the secondembodiment. An inkjet head of the third embodiment has the same basicstructure as that of the first embodiment. Therefore, in the thirdembodiment, constituent elements which are the same as those of thefirst embodiment are denoted by the same respective reference numeralsas those of the first embodiment, and explanation thereof is omitted.

As illustrated in FIG. 19, each of electrodes 60 which cover respectiveinternal surfaces of long grooves 11 is formed of a copper plating layer61 serving as a first metal layer, and a nickel plating layer 62 servingas a second metal layer. The copper plating layer 61 is an element whichforms an undercoat of the electrodes 60. The copper plating layer 61 hasa two-layer structure including an electroless copper plating layer 63 aand an electrolytic copper plating layer 63 b.

The electroless copper plating layer 63 a is superposed on an internalsurface of each long groove 11, and forms a predetermined electrodepattern for each long groove 11. The electrolytic copper plating layer63 b is superposed on the electroless copper plating layer 63 a, andcovers the electroless copper plating layer 63 a. The nickel platinglayer 62 is superposed on the copper plating layer 61, and covers thecopper plating layer 61.

The copper plating layer 61 has a function of absorbing many depressionsand projections 23 generated on the internal surface of each long groove11. Therefore, by virtue of existence of the copper plating layer 61,the nickel plating layer 62 which covers the copper plating layer 61 hasa flat surface.

Therefore, a surface 60 a of each electrode 60 which is apart from theinternal surface of the long groove 11 is flattened, and pointedprojections are removed from the surface 60 a. The surface 60 a of eachelectrode 60 has an average surface roughness of 0.6 μm or less.

The electrodes 60 are covered with an electrode protective layer 65. Theelectrode protective layer 65 has a three-layer structure including asmoothing film 66, an insulating film 67, and a protective film 68. Thesmoothing film 66 is formed of an inorganic insulating material such asSiragusital. The smoothing film 66 has a thickness such that depressionsand projections generated on the surface 60 a of each electrode 60 canbe absorbed. Therefore, a surface 66 a of the smoothing film 66 which isapart from each electrode 60 is flattened, and pointed projections areremoved from the surface 66 a. The surface 66 a of the smoothing film 66preferably has an average surface roughness of 0.6 μm or less.

The insulating film 67 is formed of an inorganic insulating materialsuch as silicon dioxide (SiO₂). The insulating film 67 is superposed onthe surface 66 a of the smoothing film 66. The insulating film 67preferably has a thickness of 1.0 μm or more.

The protective film 68 is formed of an inorganic material such ashafnium oxide (HfO₂). The protective film 68 is superposed on a surfaceof the insulating film 67, and covers the insulating film 67. Theprotective film 68 is exposed to the inside of each pressure chamber 19,and soaked in ink which is supplied to the pressure chambers 19. Theprotective film 68 preferably has a thickness of 50 nm or more.

The third embodiment is different from the first embodiment in theprocess of forming an electrode protective layer 65 on the surfaces 60 aof the electrodes 60. The other parts of the process of manufacturingthe inkjet head 1 are the same as those of the first embodiment.Therefore, in the third embodiment, only the process of forming theelectrode protective layer 65 is explained.

A smoothing film 66 is formed on electrodes 60 which are formed on theinternal surfaces of the long grooves 11. In the present embodiment, forexample, a Siragusital solution is adhered onto the surfaces 60 a of theelectrodes 60 by dipping, and thereby the smoothing film 66 is formed onthe surfaces 60 a of the electrodes 60. The smoothing film 66 is formedon the surface 60 a of each electrode 60, with a thickness such that thesurface 66 a apart from the electrodes 60 has an average surfaceroughness of 0.6 μm or less.

By virtue of the existence of the smoothing film 66 having the abovestructure, many depressions and projections generated on the surface 60a of each electrode 60 are absorbed, and the surface 66 a of thesmoothing film 66 is flattened.

Then, an insulating film 67 is formed on the smoothing film 66. Silicondioxide, which is an example of the inorganic insulating material, isused as the insulating film 67. The insulating film 67 is formed by, forexample, PE-CVD (Plasma-Enhanced Chemical Vapor Deposition). Theinsulating film 67 has a thickness of 1.0 μm or more.

The inorganic insulating material which forms the insulating film 67 isnot limited to silicon dioxide. As the inorganic insulating material, itis possible to use, for example, Al₂O₃, SiN, ZnO, MgO, ZrO₂, Ta₂O₅,Cr₂O₃, TiO₂, Y₂O₃, YBCO, mullite (Al₂O₃.SiO₂), SrTiO₃, Si₃N₄, ZrN, AlN,or Fe₃O₄.

As the method of forming the insulating film 67, it is possible to use,for example, MBE (Molecular Beam Epitaxy), AP-CVD (Atmospheric-PressureChemical Vapor Deposition), ALD (Atomic-Layer Deposition), orapplication, as well as PE-CVD. In other words, the method of formingthe insulating film 67 is not limited, as long as the inorganicinsulating material can be deposited on the smoothing film 66 byreacting or condensing the inorganic insulating material including SiO₂on the smoothing film 66 in a vacuum or the atmosphere.

When the insulating film 67 is formed, part of the conductor pattern 30which is guided to the surface of the substrate structure 41 is masked.Thereby, the insulating film 67 is prevented from being formed on thepart of the conductor pattern 30 to which a tape carrier package 31 isconnected.

Lastly, a protective film 68 is formed on the insulating film 67. Theprotective film 68 is formed by, for example, ALD (Atomic-LayerDeposition). The protective film 68 has a thickness of 50 nm or more.

As the method of forming the protective film 68, it is possible to useAP-CVD (Atmospheric-Pressure Chemical Vapor Deposition) or the like, aswell as ALD. In other words, the method of forming the protective film68 is not limited, as long as the inorganic insulating material such ashafnium oxide can be deposited on the insulating film 67 by reacting orcondensing the inorganic insulating material on the insulating film 67in a vacuum or the atmosphere.

In addition, when the protective film 68 is formed, part of theconductor pattern 30 which is guided to the surface of the substratestructure 41 is masked. Thereby, the protective film 68 is preventedfrom being formed on the part of the conductor pattern 30, to which thetape carrier package 31 is connected.

According to the third embodiment, the copper plating layer 61 whichserves as an undercoat of the electrodes 60 has a function of absorbingmany depressions and projections 23 generated on the internal surfacesof the long grooves 11, and smoothing the surfaces 60 a of theelectrodes 60. Therefore, the surface 60 a of each electrode 60 is aflat surface, from which pointed projections that cause pin holes areremoved.

In addition, the smoothing film 66 is interposed between the surface 60a of each electrode 60 and the insulating film 67. The surface 66 a ofthe smoothing film 66, which is apart from each electrode 60, is a flatsurface, from which pointed projections that cause pin holes areremoved.

Therefore, since the smoothing film 66 further exists on the surface 60a of each electrode 60, which has increased flatness, it is possible tomore securely prevent generation of pin holes in the insulating film 67and the protective film 68 which protect the electrodes 60.

As a result, it is possible to maintain electrical insulation of theelectrodes 60 from ink by using the electrode protective layer 65 havingthe three-layer structure, and avoid corrosion of the electrodes 60 andelectrical decomposition of ink. Therefore, it is possible to obtain theinkjet head 1 which has a good printing quality and excellentdurability, in the same manner as the first embodiment.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An inkjet head comprising: partition walls whichform a plurality of pressure chambers that are arranged at intervals; anozzle plate which closes an end of each of the partition walls, thenozzle plate including a plurality of nozzles that communicate with thepressure champers, each of the nozzles having a tapered shape and adiameter increased toward the pressure champers; electrodes which arearranged on the partition walls; and protective films of inorganicmaterial which are provided on side surfaces of the partition wallsdifferent from the one end of the partition walls, superposed on thepressure chambers, and soaked in ink that is supplied to the pressurechambers.
 2. The inkjet head of claim 1, wherein the partition walls areformed of a piezoelectric material.
 3. The inkjet head of claim 1,wherein the protective films are formed of a first inorganic filmsuperposed on the electrodes to cover surfaces of the electrodes, and asecond inorganic film superposed on the first inorganic film.
 4. Theinkjet head of claim 3, wherein an imaginary line extending from an edgeof the tapered shape to the pressure chambers intersects the protectivefilms.
 5. The inkjet head of claim 4, wherein an adhesive is provided,the adhesive being fixed onto one end surface of the partition walls andcontinuously provided on internal surface of the tapered shape.
 6. Theinkjet head of claim 3, wherein the second inorganic film is superposedon the pressure chambers.
 7. The inkjet head of claim 6, wherein thesecond inorganic film is a protective film.
 8. The inkjet head of claim6, wherein the protective films are formed of hafnium oxide.
 9. Theinkjet head of claim 3, wherein the second inorganic film is aninsulating film.
 10. The inkjet head of claim 3, wherein the insulatingfilm is formed of silicon dioxide.
 11. The inkjet head of claim 3,wherein the electrodes comprise a copper plating layer and a nickelplating layer.
 12. The inkjet head of claim 3, wherein a surface of eachof the electrodes which are apart from the internal surfaces of thepressure chambers is flattened.